The present invention concerns a self-pierce rivet.
Self-pierce rivets in current use have a round head and a round shank and are used in conjunction with a round setting die which has a semi-toroidal cavity and a central anvil. In a typical application the diameter of the shank would be 5 mm, the diameter of the head would be 8 mm and the diameter of the die cavity would be 9 mm.
The term "self-pierce" is normally applied to a semi-tubular rivet used to fasten incompressible materials such as metals. Because the materials are incompressible, the rivet, when applied to a workpiece, displaces a volume of workpiece material equal to the volume of the part of the rivet that enters the material. A principal function of the die is to form the displaced material into a round "button".
There is in common usage another form of self-pierce rivet, generally known as a "bifurcated" rivet. Such a rivet has a slotted shank and is not as strong as a rivet of semi-tubular construction. Consequently, it is normally used to fasten compressible materials such as wood and leather. In this case, the legs of the rivet pierce through the workpiece with far less material displacement and are caused to splay outwardly by the die, thereby securing the components of the workpiece. The die is circular in form and the rivet can be presented to it in any axially angular position.
These designs of self-pierce rivets have limitations in application in that often they cannot allow be applied in the optimum position for effective fastening. For example, when applied to flanges the ideal position for the fastener is one where the shank of the rivet is immediately adjacent to the wall of the flange. With current designs, this is not possible because the rivet head, the rolled portion of the shank, and the displaced material far beyond the shank and consequently the rivet has to be applied in a position offset from the wall. This offset reduces the structural rigidity of the riveted assembly and increases the width of the flange required for riveting.